Contrast AF and phase-difference AF have been known as automatic focusing (AF) techniques for use with an image capturing apparatus such as a digital camera. Contrast AF is an operation mode for placing a light-receiving sensor in the vicinity of an estimated focal plane, where an image of the subject entering by way of an image capturing lens is to be formed, and in the neighborhood of the estimated focal plane; detecting the amount of defocusing in accordance with a difference in the amounts of light falling on pixels adjacent to the image of the subject; and driving the lens on the basis of this result of detection, to thus bring the subject into focus. The phase-difference AF is an operation mode for detecting the amount and direction of defocus from a difference between phases of images of the subject, which are again formed by two split beams, and actuating the lens to focus on the image of the subject.
Japanese Patent Laid-Open Publication No. Hei 7-43605 discloses a technique for causing a lens to focus by means of performing coarse control through phase-difference AF and fine control through contrast AF.
Japanese Patent No. 3634232 also discloses a technique of combined adoption of phase-difference AF and contrast AF.
Contrast AF detects a peak of contrast by means of “mountain-climbing” or the like, and hence suffers a problem of focusing entailing consumption of time. The phase-difference AF requires a module for detecting a distance, provided separately from an image capturing optical system, which makes the configuration of the camera complex. Consequently, contrast AF and the phase-difference AF have their merits and demerits, and it is necessary to select one conforming to the configuration of a digital camera from the two operation modes.
Characteristics of the digital camera include compact size and a large optical zoom range. The user prefers a wider zoom range to a limited zoom range. However, when the digital camera is provided with a lens of wide zoom range without sacrificing picture quality of a captured image, the digital camera increases in size. An expensive camera, such as an optical single-lens reflex camera, can use a plurality of interchangeable lenses; e.g., a 28 mm to 70 mm zoom lens and a 70 mm to 120 mm zoom lens. However, the compact digital camera imposes an inconvenience on the user.
Accordingly, a conceivable digital camera has a plurality of image capturing optical systems having different focal lengths. However, in such a digital camera, issues arise in relation to how fast and accurately AF is performed.
The object of the present invention is to provide an image capturing apparatus which includes a plurality of image capturing optical systems having different angles of view (or focal lengths) and which can promptly and accurately detect a distance to a subject, to thus quickly perform AF operation.